U.S. patent number 9,048,949 [Application Number 13/975,299] was granted by the patent office on 2015-06-02 for controlling transmission power in an irda/rc transmitter circuit.
This patent grant is currently assigned to IXYS CH GmbH. The grantee listed for this patent is IXYS CH GmbH. Invention is credited to Daniel SauFu Mui.
United States Patent |
9,048,949 |
Mui |
June 2, 2015 |
Controlling transmission power in an IrDA/RC transmitter
circuit
Abstract
An infrared LED of an IrDA transceiver module is usable to
transmit IrDA signals as well as RC control signals. When making an
IrDA transmission, the IrDA LED is driven with a lower amount of
current. When making an RC transmission, the IrDA LED is driven
with an increased amount of current such that infrared emissions
received by an RC receiver are of adequate power to be received as
RC control signals. A current-limiting circuit allows more LED
current to flow the longer current is allowed to flow through the
IrDA LED. By controlling the durations of infrared bursts in the RC
transmission, the average LED current during infrared bursts of RC
transmissions is controlled. Using this technique allows the IrDA
module to be used to transmit RC signals at different transmission
power settings. To reduce power consumption, the minimum
transmission power necessary to engage in RC communications is
used.
Inventors: |
Mui; Daniel SauFu (San Jose,
CA) |
Applicant: |
Name |
City |
State |
Country |
Type |
IXYS CH GmbH |
Bruegg bei Biel |
N/A |
CH |
|
|
Assignee: |
IXYS CH GmbH
(CH)
|
Family
ID: |
49181519 |
Appl.
No.: |
13/975,299 |
Filed: |
August 24, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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11437884 |
May 19, 2006 |
8543002 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04B
10/114 (20130101); H04B 10/1141 (20130101); H04B
10/11 (20130101) |
Current International
Class: |
H04B
10/114 (20130101) |
Field of
Search: |
;398/106,111 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1054423 |
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May 1999 |
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EP |
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1345341 |
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Nov 2002 |
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EP |
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60178735 |
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Feb 1984 |
|
JP |
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Other References
"Interfacing the Agilent HSDL-3002 for Remote Control Operation,"
Application Note 1314 by Agilent Technologies, Inc., Feb. 18, 2003,
16 pages. (ISBN: 5988-7936EN). cited by applicant .
"Agilent IrDA Data Link Design Guide," by Agilent Technologies,
Inc., Mar. 26, 2003, 67 pages. cited by applicant .
"Agilent HSDL-3003 IrDA Data Compliant Low Power 115.2 kbit/s with
Remote Control Infrared Transceiver," Data Sheet by Agilent
Technologies, Inc., Jun. 11, 2003, 21 pages. cited by applicant
.
"Utilizing a Vishay IrDA Transceiver for Remote Control,"
Application Note by Vishay Semiconductors, Feb. 20, 2004, 14 pages.
cited by applicant .
Webpage entitled "Infrared transceivers--Vishay--Remote control
applications" downloaded on Feb. 24, 2004 from
www.vishay.com/ir-transceivers/remote-list/, 5 pages. cited by
applicant .
"TFDU6102, Fast Infrared Transceiver Module," Vishay, Nov. 2003.
cited by applicant.
|
Primary Examiner: Li; Shi K
Attorney, Agent or Firm: Imperium Patent Works Wallace; T.
Lester Wallace; Darien K.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of, and claims priority under 35
U.S.C. .sctn.120 from, nonprovisional U.S. patent application Ser.
No. 11/437,884 entitled "Controlling Transmission Power in an
IrDA/RC Transmitter Circuit," filed on May 19, 2006, the subject
matter of which is incorporated herein by reference.
Claims
What is claimed is:
1. A handheld infrared remote control (RC) device, the remote
control device comprising: an infrared transmitter circuit that
emits an infrared remote control signal that controls an electronic
consumer device, wherein the infrared transmitter circuit transmits
the remote control signal to the electronic consumer device at a
plurality of transmission power settings; and a microcontroller
that determines which one of the plurality of transmission power
settings will be used.
2. The handheld infrared remote control (RC) device of claim 1,
wherein the infrared transmitter circuit comprises: an infrared
light emitting diode (LED); a passive current-limiting circuit that
limits an LED drive current flowing through the infrared LED to a
first average current value if the remote control signal is
transmitted with bursts having a shorter first duration, whereas
the passive current-limiting circuit limits the LED drive current
flowing to a second average current value if the remote control
signal is retransmitted with bursts having a longer second
duration; and a switch for switching the LED drive current on and
off.
3. The handheld infrared remote control (RC) device of claim 2,
wherein the remote control signal has a lower transmission power
setting when transmitted with bursts having the shorter first
duration and has a higher transmission power setting when
retransmitted with bursts having the longer second duration.
4. The handheld infrared remote control (RC) device of claim 1,
wherein the remote control signal has bursts of infrared energy,
wherein each of the bursts has a burst duration, and wherein the
microcontroller changes the transmission power setting at which the
bursts of the remote control signal are transmitted by changing the
burst duration.
5. The handheld infrared remote control (RC) device of claim 1,
wherein the handheld infrared RC device does not have an IrDA
communication capability.
6. A method, comprising: (a) transmitting an infrared remote
control (RC) signal that includes a plurality of infrared bursts
from an infrared light emitting diode (LED) of a remote control
device during a key press condition using a first transmission
power setting; and (b) determining that the key press condition has
exceeded a predetermined duration, and in response to said
determining changing a burst duration to change the transmission
power setting to a second transmission power setting, wherein the
second transmission power setting is a higher transmission power
setting than the first transmission power setting.
7. The method of claim 6, wherein the changing of the transmission
power setting in (b) involves increasing the burst duration.
8. The method of claim 6, wherein both the first transmission power
setting and the second transmission power setting are sufficient to
communicate the RC signal from the remote control device to an
electronic consumer device.
9. The method of claim 6, wherein the first transmission power
setting is achieved by limiting an LED drive current that flows
through the LED by using an inductor.
10. The method of claim 9, wherein the inductor does not saturate
when the LED drive current flows through the inductor during the
second transmission power setting.
11. The method of claim 6, wherein the remote control device does
not have an IrDA communication capability.
12. The method of claim 6, wherein the first transmission power
setting is insufficient to communicate the RC signal from the
remote control device to an electronic consumer device, and wherein
the second transmission power setting is sufficient to communicate
the RC signal from the remote control device to the electronic
consumer device.
13. A handheld infrared remote control device, the remote control
device comprising: an infrared light emitting diode (LED) through
which a burst of LED drive current flows; an infrared transmitter
that emits an infrared remote control signal that controls an
electronic consumer device, wherein the infrared transmitter
transmits the remote control signal to the electronic consumer
device at a plurality of transmission power settings; and a
microcontroller that selects at which of the plurality of
transmission power settings the remote control signal is emitted by
selecting how long the burst of LED drive current flows through the
infrared LED.
14. The handheld infrared remote control device of claim 13,
wherein the plurality of transmission power settings at which the
remote control signal is transmitted includes a first power setting
in which the burst of LED drive current flows through the infrared
LED during a longer first duration and a second power setting in
which the burst of LED drive current flows through the infrared LED
during a shorter second duration, and wherein the burst of LED
drive current during the shorter second duration is sufficient to
communicate the remote control signal from the remote control
device to the electronic consumer device.
15. The handheld infrared remote control device of claim 13,
wherein the plurality of transmission power settings at which the
remote control signal is transmitted includes a first power setting
in which the burst of LED drive current flows through the infrared
LED during a longer first duration and a second power setting in
which the burst of LED drive current flows through the infrared LED
during a shorter second duration, and wherein both the first power
setting and the second power setting are sufficient to communicate
the remote control signal from the remote control device to the
electronic consumer device.
16. The handheld infrared remote control device of claim 13,
wherein the microcontroller includes a switch that is conductive
during a mark time of the remote control signal.
Description
TECHNICAL FIELD
The present disclosure relates to controlling transmission power in
infrared communications.
BACKGROUND INFORMATION
Portable electronic devices such as personal digital assistants
(PDAs), cell phones, digital cameras, MP3 players, and laptop
computers often use a type of infrared transceiver called an IrDA
(Infrared Data Association) transceiver to transfer information.
Each IrDA transceiver has an infrared light emitting diode (LED)
that emits infrared radiation having a center wavelength somewhere
in the range of from 850 nm to 900 nm (for example, 875 nm). Each
IrDA transceiver also has an IR receiver (for example, a PIN diode)
for receiving infrared signals of this wavelength. If, for example,
each of two such portable electronic devices has an IrDA
transceiver, then one device can transmit data to the other device
across an IrDA link using infrared signals that comply with an IrDA
standard. IrDA is, for example, often employed to communicate files
of digital information between portable devices having such IrDA
transceivers.
Electronic consumer devices in the home such as televisions, VCRs,
DVD players, DVRs, CD players, stereo equipment, home theatre
equipment, and so forth are typically controlled by remote control
(RC) devices that also transmit infrared signals. These ordinary
infrared signals, referred to here as "RC" (or remote control)
infrared signals, typically have a center wavelength somewhere in
the range of from 900 nm to 950 nm (for example, 940 nm). To turn
the power on to a television, for example, a user may press a power
key on a remote control device. The remote control device has an
infrared LED that emits an RC infrared signal to the television. An
infrared RC receiver circuit in the television receives the RC
infrared signal, decodes the signal, and responds by turning the
television on.
It has been recognized that it would be desirable to be able to use
a portable electronic device to control an electronic consumer
device that is designed to respond to RC infrared signals. If, for
example, a user had a cellular telephone in his/her hand, then the
user could use the cellular telephone to control a television.
It has been recognized that an IrDA transmitter LED within an IrDA
transceiver module can be used as an infrared transmitter both for
IrDA and RC applications. Although the peak wavelength of the
transmitter LED in the IrDA transceiver is at a wavelength that is
different from the wavelength of peak sensitivity of the RC
infrared receiver in the electronic consumer device, some radiation
transmitted by the infrared transmitter is nevertheless received by
the RC receiver. The IrDA transmitter transmits energy in a band
and the RC receiver receives energy in a band. The two bands
overlap. Due to the mismatch of the center transmitter and receiver
wavelengths, however, it may be necessary for the IrDA transmitter
LED power to be increased in order for enough energy to be received
at the RC receiver for the communication to work properly. An
application note from Vishay Semiconductors (Vishay Semiconductor
Application Note entitled "Utilizing a Vishay IrDA Transceiver for
Remote Control", document number 82606, 14 pages, Feb. 20, 2004)
discloses reducing the value of a current-limiting resistor so as
to increase IrDA LED transmitter peak current and thereby to
increase emission intensity of the IrDA LED transmitter.
Improvements and enhancements to a system employing an IrDA
transceiver to transmit infrared signals to an RC receiver are
sought.
SUMMARY
The same infrared light emitting diode (LED) of an (Infrared Data
Association) IrDA transceiver module is usable both to transmit
IrDA communication signals as well as to transmit infrared signals
that are usable as remote control (RC) signals to control an
electronic consumer device. When making an IrDA transmission, the
IrDA LED is driven with a lower amount of current appropriate for
IrDA communication. When making an RC transmission, the IrDA LED is
driven with an increased amount of current such that infrared
emissions received by an RC receiver within the electronic consumer
device are of adequate power to be received as RC signals. A
current-limiting circuit allows more LED current to flow the longer
current is allowed to flow through the IrDA LED. By controlling the
durations of infrared bursts in the RC transmission, the average
LED current during infrared bursts of the RC transmission is
controlled. Longer infrared bursts have larger average LED
currents. Shorter infrared bursts have smaller average LED
currents. Using this technique of controlling the durations of
infrared bursts to control transmission power allows the IrDA
module to be used to transmit RC signals at different power
settings. RC signals having a higher power setting involve infrared
bursts of longer duration. RC signals having a lower power setting
involve infrared bursts of shorter duration. To reduce power
consumption in the RC mode, the transmission power setting of the
minimum transmission power necessary to engage in RC communications
is used.
In one novel aspect, a portable electronic device (for example, a
cell phone, a PDA, an MP3 player, a digital camera, or a laptop
computer) includes the IrDA transceiver module and the
current-limiting circuit described above. The IrDA LED of the IrDA
transceiver module within the portable electronic device is usable
to transmit RC signals to an electronic consumer device (for
example, a television) of a user, but the user does not have
codeset information for generating appropriate RC control signals
for the particular electronic consumer device. The user therefore
takes the portable electronic device to a location that dispenses
RC codeset information. The location may, for example, be an
electronic store that disseminates RC codeset information. The IrDA
transceiver module of the portable electronic device is then used
to engage in IrDA communications to download RC codeset information
from another IrDA device maintained by the store. The RC codeset
information is codeset information for controlling the user's
electronic consumer device. Once the RC codeset information has
been downloaded into the portable electronic device, the user takes
the portable electronic device home and uses the IrDA LED of the
transceiver in the portable electronic device in combination with
the current-limiting circuit to transmit RC signals (such an RC
signal is sometimes referred to as an "RC operational signal") from
the portable device to the electronic consumer device. The RC
signals are generated using the downloaded RC codeset information
and therefore are usable to control the electronic consumer device.
The transmission power of the RC signals is selected or adjusted or
controlled as described above by selecting, adjusting or
controlling the durations of the infrared bursts within the RC
signals. Where, for example, the remote control device involves a
microcontroller that drives a digital control signal TX to the IrDA
transceiver module top turn off and on a switch within the IrDA
module, the microcontroller sets the durations of the pulses (pulse
widths) of the control signal TX so that the resulting RC signal
that is transmitted from the IrDA transceiver module is of the
appropriate power setting. By changing the power setting of the RC
transmissions, the transmission range of the remote control device
can be changed. By maintaining the power setting of the RC
transmissions at as low a setting as is necessary for proper
communication, power consumption of the remote control device is
reduced.
Other embodiments and advantages and considerations and methods are
described in the detailed description below. This summary does not
purport to define the invention. The invention is defined by the
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
The accompanying drawings, where like numerals indicate like
components, illustrate embodiments of the invention.
FIG. 1 is a diagram of an IrDA (Infrared Data Association) circuit
1 within a portable electronic device in accordance with one novel
aspect. The duration of an infrared burst determines the average
LED drive current during the burst, and therefore also determines
the average transmission power during the burst.
FIG. 2 is a perspective view of the IrDA transceiver module in
circuit 1 of FIG. 1.
FIG. 3 is cross-sectional side view of the IrDA transceiver module
of FIG. 2.
FIG. 4 is a cross-sectional top-down view of the IrDA transceiver
module of FIG. 2.
FIG. 5 is a graph that shows a spectral emission distribution curve
of an infrared LED within an IrDA transceiver module as well as a
composite spectral sensitivity curve for numerous typical IR remote
control (RC) receivers.
FIG. 6 is a diagram that shows how increased current flow through
infrared LED of an IrDA transceiver module will cause the LED to
output enough energy at 900 nm for RC receiver operation.
FIG. 7 shows waveforms of signals that can be output from the IrDA
transceiver module of FIG. 1.
FIG. 8 is a waveform diagram that illustrates how the average LED
drive current through the infrared LED of the IrDA transceiver
module of FIG. 1 can be controlled in the RC mode to change the
average LED drive current flowing through the LED during an
infrared burst during generation of an RC control signal. The
smaller average LED drive current on the left side of FIG. 8
represents a lower transmission power setting. The higher average
LED drive current on the right side of FIG. 8 represents a higher
transmission power setting.
FIG. 9 (Prior Art) is a diagram of a conventional LED drive circuit
that is part of an ordinary held-held RC remote control device of
the type used to control consumer electronic appliances in the
home.
FIG. 10 is a diagram of a current-limiting circuit in an RC remote
control device in accordance with a second novel aspect.
FIG. 11 is a flowchart of a method in accordance with another novel
aspect.
DETAILED DESCRIPTION
Reference will now be made in detail to some embodiments of the
invention, examples of which are illustrated in the accompanying
drawings.
FIG. 1 is a diagram of an IrDA (Infrared Data Association) circuit
1 within a portable electronic device in accordance with one novel
aspect. Circuit 1 includes an IrDA transceiver module 2, a passive
LED drive current-limiting circuit 3, a central processing unit
(CPU) 4, and an operating system 5. The operating system has access
to IR remote control (RC) codeset information 6. IrDA transceiver
module 2 is disposed on a printed circuit board. In the present
example, the portable electronic device of which the IrDA
transceiver module 2 is a part is a personal digital assistant
(PDA) and the printed circuit board is the printed circuit board of
the PDA. Passive LED drive current-limiting circuit 3 includes a
first resistor 7 that is coupled in parallel with a series
combination of an inductor 8 and a second resistor 9. First
resistor 7, inductor 8, and second resistor 9 are all discrete
components disposed on the printed circuit board.
FIG. 2 is a perspective view of IrDA transceiver module 2. FIG. 3
is a cross-sectional side view of IrDA transceiver module 2 of FIG.
2. FIG. 4 is a top-down view of a cross-section of IrDA transceiver
module 2 of FIG. 1. IrDA transceiver module 2 may be an IrDA module
of conventional construction such as an IrDA module available from
Zilog, Inc. of San Jose, Calif. The IrDA module 2 includes three
dice: 1) an IR transmitter diode die 10, 2) an IR receiver PIN
diode die 11, and 3) a controller die 12. The three dice are
mounted on a very small printed circuit board 13. Molded plastic 14
covers the printed circuit board and die assembly and forms two
semi-spherical lenses 15 and 16. Lens 15 is the receiver lens that
focuses incoming IR radiation 17 onto the PIN receiver diode 11
with the module. Lens 16 redirects the radiation emitted from IR
transmitter LED die 10 into a beam 18.
Returning to FIG. 1, when an IrDA transmission is to occur, the 875
nm transmitter LED 10 is controlled in the conventional IrDA
manner. In one example, an IrDA TX signal is supplied to the IrDA
module via an IrDA/RC TX terminal 19 on the IrDA module, and an
IrDA driver switch portion 20 of controller die 12 switches current
through LED 10 in conventional fashion. IrDA driver switch portion
20 in this example is a field effect transistor. The amount of LED
drive current initially when current starts to flow through LED 10
is limited primarily by the first resistor 7 in the left leg of the
current-limiting circuit. The resistance of first resistor 7 is
approximately one ohm. The IrDA TX signal stops drawing current
through LED 10 before significant current begins to flow through
inductor 8 in the right leg of the current-limiting circuit. The
average LED drive current is therefore approximately 265 mA (over
one IR burst duration), and the resulting intensity of radiation
emitted from IrDA module 2 is approximately 40 mW/sr at 875 nm.
When a remote control (RC) transmission is to occur, however, a
digital RC control signal TX is generated by software executing on
the CPU 4 using the codeset information 6. For additional detail on
codesets, on how codesets can be stored, and on an exemplary way to
generate an RC transmission from codeset information, see: U.S.
patent application Ser. No. 10/777,023, filed Feb. 10, 2004, now
U.S. Pat. No. 7,259,696; and U.S. Pat. No. 7,339,513, filed Aug.
27, 2004 (the entire subject matter of these two documents is
incorporated herein by reference). No microcontroller that stores
codeset information need be provided where the IrDA circuit 1 is
part of a personal digital assistant (PDA). Rather, codeset
information 6 is stored in main memory on the PDA such that
software executing on the CPU 4 of the PDA can access the codeset
information and use it to drive the IrDA/RC TX terminal 19 with the
RC TX signal. This RC TX signal is provided to IrDA module 2 via
the same IrDA/RC TX terminal 19 that is used to supply the IrDA TX
signal. Although an RC infrared signal is to be transmitted,
transmitter LED 10 has a transmission peak at 875 nm. An IR remote
control receiver (not shown) on an electronic consumer device (not
shown) that is to be controlled by the RC transmission has a peak
spectral sensitivity at a wavelength of approximately 940 nm. It is
recognized that most IR remote control receivers in electronic
consumer devices will work satisfactorily if they receive 40
mW/steradian at 940 nm.
FIG. 5 is a graph that shows the spectral emission distribution
curve 21 of 875 nm IrDA transmitting LED 10 as well as a composite
spectral sensitivity curve 22 for numerous typical IR remote
control (RC) receivers. Note that the amount of radiation emitted
from the 875 nm transmitting diode 10 drops from its normalized
high at 875 as wavelength increases to the right of its peak. The
amount of radiation emitted is down to sixty percent of its
normalized high at 900 nm. Also note that the spectral sensitivity
of the composite IR remote control (RC) receiver curve is at its
normalized high at 940 nm, but that it is down to seventy percent
of its high at 900 nm to the left of its peak. The curve 21 of the
IrDA transmitter LED overlaps the response curve 22 of the RC
receiver.
Although IrDA uses an infrared signal of approximately 870 nm and
RC remote control devices use an infrared signal of approximately
960 nm, the IrDA transmitter LED within module 2 actually emits
radiation over a range of wavelengths. By increasing the
transmission power of the IrDA LED 10, the amount of energy
transmitted at 960 nm can be made sufficiently large that the IrDA
transmitter LED is usable to make RC transmissions to an RC
receiver. See United States Publication 2005/0185962, published
Aug. 25, 2005, and United States Publication 2006/0018662,
published Jan. 26, 2006 (the entire subject matter of these two
publications is incorporated herein by reference).
FIG. 6 is a diagram that shows how increased current flow through
the IrDA 875 nm transmitter diode 10 in the RC transmitter mode
will cause IrDA module 2 to output enough energy at 900 nm for RC
receiver operation.
The circuit of FIG. 1 works by taking advantage of the fact that RC
signals are transmitted with longer bursts of IR energy
(approximately 10 microseconds) whereas the IrDA signals are
transmitted with shorter bursts of IR energy (approximately 1.6
microseconds). During a short IrDA burst, inductor 8 of the passive
LED drive current-limiting circuit 3 of FIG. 1 is not conducting a
significant amount of current. Current flow through the passive LED
drive current-limiting circuit 3 is limited primarily by the
current-limiting first resistor 7 in the left leg of the
current-limiting circuit 3. The value of the first resistor 7 is
selected to limit the current flow into the LED 10 to a relatively
low current level suitable for the IrDA transmission.
During a relatively longer RC burst, inductor 8 of the
current-limiting circuit 3 of FIG. 1 conducts larger and larger
amounts of current. If the magnetic field were to build up in
inductor 8 until the core of inductor 8 were to saturate, then
current flow through the current-limiting circuit 3 would level off
at a current determined by the equivalent parallel resistance of
first resistor 7 and second resistor 9 in the right leg of the
current-limiting circuit 3. This peak amount of current would be
the current flow into the LED 10 during the RC transmission.
In accordance with one novel aspect, an amount of IR energy
transmitted by LED 10 per RC infrared burst is selected, adjusted
and/or controlled by CPU 4 of the PDA. FIG. 7 is a diagram that
shows waveforms of signals in accordance this novel aspect. In the
IrDA mode (illustrated in the portions of the waveforms on the left
side of the page), the IR burst duration is so short that inductor
8 in the right leg of the current-limiting circuit 3 (see FIG. 1)
has not begun to conduct significant current by the time the end of
the burst occurs. Current flow through LED 10 is therefore limited
by the first resistor 7 in the left leg of the current-limiting
circuit as set forth above in connection with FIG. 1. The IrDA
transmission is not modulated with a sub-carrier. The average
current that flows into and through LED 10 is approximately 195 mA
average during an IR burst duration in the IrDA mode. The current
flows from the supply voltage conductor, through current-limiting
circuit 3, through LED 10, through the switch in IrDA driver 20,
and to a ground potential conductor.
RC mode operation is illustrated in the portion of the waveforms on
the right side of FIG. 7. The 1.2 millisecond mark times of the RC
signal illustrated in the upper waveform are modulated with a
sub-carrier (sometimes referred to as the "carrier"). The second
row of waveforms shows this modulation of the RC signal in greater
detail. Individual bursts of IR are approximately 8 microseconds
long. There are 32 microseconds between successive bursts. Due to
the longer duration of an IR burst in the RC mode (in the
illustrated example, eight microseconds), the inductor 8 begins to
conduct current during a burst period. LED drive current rapidly
rises until the end of the IR burst as illustrated. Inductor 8 is
not yet saturated at the time that the IR burst ends in the RC
example at the right of FIG. 7. Accordingly, the LED current of the
waveform second from the bottom continues to rise through the
duration of the IR burst. The average LED current is approximately
400 mA during an IR burst in the RC example at the right of FIG.
7.
FIG. 8 illustrates how the average LED drive current through LED 10
during an IR burst is set, controlled and/or controlled in the RC
mode in the novel aspect. The average current flowing into LED 10
is increased by increasing the duty cycle of the RC sub-carrier.
This is done by increasing the duty cycle of the controlling TX
signal on IrDA/RC TX terminal 19. The resulting IR burst on the
left side of the diagram of FIG. 8 is the same eight microsecond
burst illustrated in FIG. 7. It was generated by a TX control
signal of a duty cycle of 8 to 32, where the period of the
sub-carrier is the 40 microseconds. The average LED drive current
is 400 mA during the burst time.
The burst on the right side of FIG. 8 is, however, generated by a
TX control signal of a duty cycle of 18 to 22, where the period of
the sub-carrier is the same 40 microseconds. Rather than stopping
the IR burst at the time when the current flowing through the
current-limiting circuit 3 has risen to 600 mA as in the burst on
the left side of the diagram of FIG. 8, the IR burst is extended
such that the LED drive current flowing through the
current-limiting circuit 3 continues to rise. The duration of the
IR burst in the example on the right side of FIG. 8 is 18
microseconds. The average LED drive current is 550 mA during the
burst. It is therefore seen that increasing the duty cycle of the
TX control signal results in a higher average LED drive current
flowing through LED 10 during a burst time. It also results in a
higher average LED drive current flowing through the LED 10 when
the entire mark time is considered.
Changing the duty cycle of the sub-carrier of the TX control signal
during the RC mode does not generally disrupt receipt of the RC
signal by typical receivers in typical electronic consumer devices.
RC receivers are generally tuned to the frequency of the
sub-carrier, not to the duty cycle of sub-carrier. Note that in
both the low average transmission power situation at the left of
FIG. 8 and in the high average transmission power situation at the
right of FIG. 8, that the period of the sub-carrier is the same 40
microseconds.
The use of current-limiting circuit 3 involving inductor 8 and the
changing of the duty cycle of the sub-carrier to increase RC LED
drive current during IR bursts is not limited to use with an IrDA
transceiver module or with IrDA. FIG. 9 (Prior Art) is a diagram of
a conventional 960 nm LED drive circuit that is part of an ordinary
hand-held RC remote control device of the type used to control
consumer electronic appliances in the home. The LED drive current
100 flowing through 960 nm LED 101 is fixed by the resistance of
the current-limiting resistor 102.
FIG. 10 is a diagram of a current-limiting circuit 200 in an RC
remote control device in accordance with a second novel aspect.
Average LED drive current 201 flowing through a 960 nm LED 202
during an IR burst of an RC signal is controlled by controlling the
duty cycle of the RC sub-carrier signal. IR bursts of longer
duration have a higher average LED drive current. The
microcontroller of the RC remote control device that typically
drives the TX control signal to the LED 202 can, with minimal
additional complexity, be made to set and/or change and/or control
the duty cycle of the sub-carrier of the IR bursts in order to
increase and/or decrease the average LED drive current 201 during a
burst. The RC remote control device may, for example, have two or
more different LED transmission power settings. When the first
setting is used, the IR bursts are longer and are therefore of a
higher first average transmission power. When the second setting is
used, the IR bursts are shorter and are therefore of a lower second
average transmission power. In one example, the remote control
device of the second novel aspect of FIG. 10 is an RC remote
control device that does not involve an IrDA transceiver module and
that does not and cannot transmit IrDA communication signals.
In a first method, a low transmission power setting is attempted
initially. The user of an RC remote control device may, for
example, initiate this condition by putting the remote control
device into a programming mode, and then pressing an appropriate
key on the remote control and holding it down. A microcontroller of
the remote control device then increases the transmission power
setting step by step until the user notices that the RC
communication link starts to operate in a satisfactory manner. The
microcontroller does this by increasing the duty cycle of the
sub-carrier of the RC signal. Once satisfactory RC communication is
achieved, then the increasing of power setting is halted and higher
transmission power settings are not attempted. The user may, for
example, stop the power setting from increasing by releasing the
key. In this way, if a higher average power transmission setting is
not required, then the high transmission power setting is not used
and power is saved by using the lowest power setting that functions
acceptably.
In a second method, a high transmission power setting is used
initially. The user of the RC remote control device can initiate
this condition by putting the remote control device into a
programming mode, and then pressing an appropriate key and holding
it down. The microcontroller of the remote control device then
reduces the transmission power setting step by step until the user
notices that the RC communication link has stopped functioning
satisfactorily. In one example, proper functioning can involve
turning the electronic consumer device off and then back on. The
microcontroller reduces the transmission power setting by reducing
the duty cycle of the RC signal's sub-carrier. The user may
indicate that the RC communication link has stopped functioning by
releasing the key on the RC remote control device. Releasing the
key causes the RC remote control device to increase its
transmission power setting one increment and then to use this power
setting for subsequent operation. Regardless of how the
transmission power setting is set, the transmission power setting
is selected to be the setting of the least transmission power that
works satisfactorily. As compared with a conventional RC remote
control device that has only one power setting and consequently may
use more transmission power that is required in a given
circumstance, the novel RC remote control device uses the smallest
amount of LED drive current required that results in satisfactory
communication between the RC remote control device and the
electronic consumer device to be controlled. By reducing the amount
of transmission power used, battery life of the remote control
device is extended. This control of RC transmission power sees use
in RC remote control devices that do not have an IrDA communication
capability as well as in electronic devices that employ IrDA
transceivers to transmit RC infrared signals.
In a third method, a remote control device uses a particular first
transmission power setting (step 300). If the user presses a key on
the remote for less than a predetermined normal duration, then the
first transmission power setting is used for the duration of the
key press. If, however, the user presses a key for more than the
predetermined duration (step 301), then the microcontroller
automatically increases the transmission power setting (step 302).
The transmission power setting may, for example, be increased to
the maximum transmission power setting for the entire remainder of
the key press duration or for subsequent short time periodic
intervals during the remainder of the key press duration. The
feature of automatically increasing the transmission power setting
during unusually long key presses may be usable to prevent users
from becoming irritated with a remote control device whose power
setting is so low that communication is sometimes marginally
functional and sometimes, depending on the orientation of the
remote control device and the electronic consumer device, is
nonfunctional at the low power setting.
In an embodiment where the portable electronic device (for example,
a cell phone, a PDA, an MP3 player, a digital camera, a laptop
computer) includes an IrDA transceiver module that is usable to
send RC control signals to an electronic consumer device, (for
example, a television), the user may not have codeset information
for generating control signals for the user's electronic consumer
device. In one novel aspect, the user takes the portable electronic
device to a location that dispenses codeset information. The
location may, for example, be an electronic store that disseminates
codeset information. The IrDA transceiver module of the portable
electronic device is then used to download codeset information from
another IrDA device maintained by the store. The codeset
information is codeset information for controlling the user's
electronic consumer device. The user may test usage of the RC
codeset at the location. Once the codeset information has been
downloaded into the portable electronic device, the user takes the
portable electronic device home and uses the IrDA LED of the
transceiver in the portable electronic device in combination with
the current-limiting circuit described above to transmit RC control
signals from the portable device to the electronic consumer device.
The RC control signals are generated using the downloaded codeset
information and therefore control the electronic consumer
device.
In one embodiment, a microcontroller of a remote control device
monitors the voltage level of the LED supply voltage. The LED
supply voltage is usually a battery voltage VBAT and the remote
control device is powered by the battery. Ordinarily, the
transmission power of the LED of the remote control device would
decrease with decreasing supply voltage. In this embodiment,
however, the microcontroller detects the decreasing LED supply
voltage, and increases the duty cycle of the carrier to compensate
such that LED transmission power is higher than it otherwise would
be. In one example, the compensation is adequate to maintain RC
transmission power at a substantially constant level despite a
decrease in LED supply voltage as the battery of the remote control
device ages.
Although the present invention has been described in connection
with certain specific embodiments for instructional purposes, the
present invention is not limited thereto. A current-limiting
circuit can be placed in the current supply path of another type of
radiation emitting device (for example, an LED of a flashlight or
light fixture or another type of light), and the burst duration can
be controlled to increase or decrease the average drive current
flowing through the emitting device during the on-time of the
emitting device. The burst duration can be controlled by supplying
a control signal onto a control terminal of a transistor that draws
current through the emitting device. A microcontroller or other
suitable signal generating device is usable to control and/or
change the duty cycle of the control signal, thereby controlling
and/or changing the duty cycle of the drive current flowing through
the emitting device. Increasing the duty cycle increases the
average drive current flowing through the emitting device.
Decreasing the duty cycle decreases the average drive current
flowing through the emitting device. The emitting device need not
be a light transmitting device but rather can be a transmitter of
another type of energy such as, for example, an RF transmitter. The
technique of increasing transmitting power of an emitter typically
used in a first communication band such that side skirt emissions
of the emitter are of adequate power to be received as an
intelligence signal in another communication band is not limited to
using an IrDA LED to transmit RC control signals. The particular
circuitry illustrated in FIG. 1 for the current-limiting circuit is
only exemplary. The series resistance of the right leg need not be
provided by a separate component but rather can be the series
resistance of inductor 8. Other circuit configurations for
accomplishing the function of the current-limiting circuit can be
employed. A current-limiting circuit can involve a transistor or
other mechanism for switching in different current limiting
resistances. For example, the series resistance of the right leg of
the current-limiting circuit 3 can have controlled resistance that
is a function of the burst duration setting. The cost of providing
a remote control device having multiple selectable transmission
settings is low because the capability can be provided without the
addition of a significant amount of complexity or expensive active
circuitry. The feature can, for example, be provided by adding only
a few discrete passive components (the passive current-limiting
circuit 3 of FIG. 1) and by programming the microcontroller or CPU
of the remote control device to change the pulse width of the
digital RC control signals output to the infrared LED.
Accordingly, various modifications, adaptations, and combinations
of various features of the described embodiments can be practiced
without departing from the scope of the invention as set forth in
the claims.
* * * * *
References